• Loren N Riedy, Miri Kim, Jonathan J Yun, Ewa Borys, and Vikram C Prabhu.
• Department of Neurological Surgery, Loyola University Medical Center, Maywood, Illinois, USA.
• World Neurosurg. 2019 Dec 1; 132: 239-244.

BackgroundMalignant transformation of a mature intracranial teratoma into an adenocarcinoma is an extremely rare event and portends a poor prognosis. The clinical progression, radiographic changes, histopathological findings, and immunohistochemistry findings from these unique cases might provide clues regarding this transformation. Caudal homeobox gene-2 (CDX-2) is a specific and robust marker for colonic adenocarcinomas and can also be used to identify differentiation of mature intracranial teratoma into colonic-type adenocarcinoma. To the best of our knowledge, this is the first case report of the use of this specific marker for an intracranial malignancy.Case DescriptionWe present the case of a 55-year-old right-handed Hispanic-American woman with progressive headaches who was found to have a left posterior parietotemporal tumor with intraventricular extension. Surgical debulking was performed, and the pathologic examination revealed a mature teratoma. Despite surgical resection and radiotherapy, the teratoma progressed to a malignant mature intracranial teratoma both radiographically and histologically. Histological analysis of the third specimen revealed a moderately differentiated adenocarcinoma. The tumor cells were positive for CDX-2 and cytokeratin 20 and negative for cytokeratin 7 and thyroid transcription factor-1, consistent with an enteric/colonic-type adenocarcinoma, demonstrating progressive atypia and malignancy.ConclusionsMalignant transformation of a mature intracranial teratoma portends a poor prognosis. The exact histopathological diagnosis can facilitate treatment of these patients. CDX-2 is a specific robust marker for identifying differentiation of a mature intracranial teratoma into a colonic adenocarcinoma. This positive staining can also be observed in primary colonic and other adenocarcinomas. To the best of our knowledge, this is the first report of the use of CDX-2 in the diagnosis of an intracranial malignancy. The triangulation of clinical progression, radiographic findings, and histopathological and immunohistochemistry findings provided clues regarding this unique transformation.Copyright © 2019 Elsevier Inc. All rights reserved.

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